Inorganic nano-particle and xerogel-based anti-reflection (or anti-reflective) coatings (ARCs), produced using sol-gel chemistry wet deposition techniques, typically suffer from poor “green” film (i.e., gelled, but still wet) mechanical and chemical durability, which results in fragile coatings that must be handled with great care prior to fully curing through high temperature thermal processing.
The lack of durability of the coatings at this stage or processing are due to the weak bonding (e.g., dominantly H-bonding) found in the green films, the low interfacial contact area between the spherical or/and elongated nano-particles that form the film and between the coating and the substrate (i.e., the interfacial contact area), and the open porosity which is typical of such coatings.
The low interfacial contact area and open porosity often result in coatings with poor durability even after thermally curing, as sufficient temperatures for adequately sintering the nano-particle or xerogel coatings requires processing temperatures which exceed the acceptable limits for the glass substrates to which these coatings are typically applied. Polymeric sol-gel binders have been used to improve both the green and cured film strength by acting as a cement between the various contact points and increase the effective interfacial area. However, such binders typically reduce the porosity of the coatings, thus increasing the refractive index.
Additionally, poor conformality is often exhibited by most xerogel anti-reflection coatings, which limits performance on textured glass substrates often used in photovoltaic applications. Further, xerogel anti-reflection coatings require expensive organic solvent-based formulations to be compatible with the sol-gel chemistry used to form the nano-particle film or the binder, which often produce volatile organic carbon (VOC) emissions and hazardous waste (e.g., fire hazards, toxic hazards, etc.).